drought Flashcards
what is a drought
an area of land that has been dried out,
it is a natural disaster of below-average precipitation in a given region, resulting in prolonged shortages in the water supply,
physical causes meteorological (1)
El Nino a normal condition is trade winds pushing warm waters from east to west causing low pressure, this affects countries near the equator el Nino is reversed of this where it causes low pressure in the west e.g. Australia
el Nino in Australia 2006
the lowest rainfall season since 1990s
river Maury was dried out in some places/1000 migrated
human management was poor so it excaccebtaed the drought
air pollution in the Sahel (2)
aerosol used for cleaning products that now get into the atmosphere are causing the earths northern hemisphere to cool. the Sahel is in the northern hemisphere so rainfall band the itcz caused to shift to the south where it brings them rain put prolongs rainfall for the north
10,000 people died in the Sahel between the 70s
25%of livestock died
ITCZ (1)
the band located near the equator, where northeast and southeast trade wind converge
moves up and down seasonally affecting the amount of rainfall a country gets as well as sunlight
El is in the north so when the ITCZ moves south it goes without rain for a prolonged time living possibility of drought especially as its already a semiarid event
human factors DEFORESTATION
slash and burn causes soil erosion where the top layer of the soil is displaced or worn away drying out the soil. creating cracks this will, therefore, leave for the sunlight to further dry it out, farmers lose their crops as vegetation won’t grow- Eritrea and Ethiopia were impacted badly as 10 million needed water and food assistance
overgrazing
of livestock by subsistence farmers which also leads to the removal of vegetation, this means less mean of interception from the sun allowing the soil to dry up
construction of dams
can cause drought as it reduces water flow downstream causing some areas to suffer with no water and to some extent dry out and cause a drought. however it can be necessary as it produces hydroelectric power and can produce water for farmers
water surplus?
this is when the input of precipitation is greater than what can be carried by stores or normal drainage system which can cause flooding over overload
human factors of surplus urbanisation
deforestation
this means more in the creation of impermeable rocks such as concrete being used for roads, houses which means increases surface runoff straight into the river creating a flashy river regime (short lag time between peak rainfall and time it takes to reach river)Sheffield 2007 where rain went straight into residential areas 35,000 homes flooded
no interception= soil gets really saturated very fast =surface runoff 20% of the Amazon already gone
physical factors flash flood
this is immediate unpredicted heavy rainfall e.g. Carlisle 2005 flooding two months worth of rainfall occurred in 24h killed 3 people left 2700 homeless as well as many losing their jobs it was further exacerbated by poor river hard engineering management
snowmelt Jakulluploup
this is an increase in air temperature coming into spring causes rapid snowmelt especially in mountainous areas as surface runoff leads it straight into river rising its volume causing a flood Iceland glacial outburst due to volcanic activity
